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A new class of electrolytes have been reported, hybridizing aqueous with non-aqueous solvents, which combines non-flammability and non-toxicity characteristics of aqueous electrolytes with the superior electrochemical stability of non-aqueous systems. Here, we report measurements of the structure of an electrolyte composed of an equal-mass mixture of 21 m LiTFSI-water and 9 m LiTFSI-dimethyl carbonate using high-energy x-ray diffraction and polarized neutron diffraction with isotope substitution. Neutron structure factors from partially and fully deuterated samples exhibit peaks at low scattering vector Q that we ascribe to long-range correlations involving both solvent molecules and TFSI− anions. We compare both sets of measurements with results of molecular dynamics simulations based on a polarizable force field. The structures derived from simulations are generally in agreement with those measured, except that neutron structure factors predicted for two partially deuterated samples show very intense scattering increasing up to the low- Q limit of simulation, indicating a partial segregation between the two solvents not observed in experimental measurements.

We report a systematic diffraction study of two “water-in-salt” electrolytes and a “water-in-bisalt” electrolyte combining high-energy X-ray diffraction (HEXRD) with polarized and unpolarized neutron diffraction (ND) on both H(2)O and D(2)O solutions. The measurements provide three independent combinations of correlations between the different pairs of atom types that reveal the short- and intermediate-range order in considerable detail. The ND interference functions show pronounced peaks around a scattering vector Q ∼ 0.5 Å(−1) that change dramatically with composition, indicating significant rearrangements of the water network on a length scale around 12 Å. The experimental results are compared with two sets of Molecular Dynamics (MD) simulations, one including polarization effects and the other based on a non-polarizable force field. The two simulations reproduce the general shapes of the experimental structure factors and their changes with concentration, but differ in many detailed respects, suggesting ways in which their force fields might be modified to better represent the actual systems.

Neutron diffraction with isotopic substitution (NDIS) experiments were done on both natural abundance potassium and isotopically labeled 41KCl heavy water solutions to characterize the solvent structuring around the potassium ion in water. Preliminary measurements suggested that the literature value for the coherent neutron scattering length (2.69 fm) for 41K was significantly in error. This value was remeasured using a neutron powder diffractometer and found to be 2.40 fm. This revision increases significantly the contrast between the natural abundance K and 41K by about 30% (from 1.0 to 1.3 fm). The experimentally determined structure factor of the potassium ion was then compared to that calculated from molecular dynamics (MD) simulations. Previous neutron scattering measurements of potassium gave a solvation number of 5.5 (see below). In this study, the NDIS and MD results are in good agreement and allowed us to derive a coordination number of 6.1 for water molecules and 0.8 for chloride ions around each K+ ion in 4 molal aqueous KCl solution.

"Water-in-salt" (WIS) and "water-in-bisalt" (WIBS) electrolytes have recently been developed for Li-ion batteries, combining the safety and environmental friendliness of aqueous electrolytes with a larger operating window made possible by a solid-electrolyte interphase. We report quasielastic neutron scattering (QENS) measurements on solutions of a WIS electrolyte at two concentrations, 13.9 and 21 m (molal) lithium bis(trifluoromethane)sulfonimide LiTFSI in H2O/D2O and a WIBS electrolyte at (21 m LiTFSI + 7 m lithium triflate (LiOTf)) in H2O/D2O. The data were Fourier transformed to obtain experimental intermediate scattering functions (ISFs) and compared with corresponding quantities obtained from molecular dynamics (MD) simulations. Both QENS and MD ISFs could be fitted well by a single stretched exponential function to obtain apparent translational diffusion coefficients for the water molecules. The QENS values agree well with the MD simulations for the 13.9 and 21 m solutions, but MD simulations predict a slower relaxation of water compared to QENS for the WIBS electrolyte. Comparison of the incoherent and coherent scattering reveals much faster water dynamics compared with structural relaxation of the ionic framework, consistent with the nanodomain picture where the lithium diffusion occurs through the tortuous water domain around the slower relaxing ionic matrix, leading to highly non-Gaussian water motion.

Insight into the molecular interactions of homotactic and heterotactic association of caffeine and pyridine in aqueous solution is given on the basis of both experimental and simulation studies. Caffeine is about 5 times more soluble in a 3 m aqueous pyridine solution than it is in pure water (an increase from ∼0.1 m to 0.5 m). At this elevated concentration the system becomes suitable for neutron scattering study. Caffeine-pyridine interactions were studied by neutron scattering and molecular dynamics simulations, allowing a detailed characterization of the spatial and orientational structure of the solution. It was found that while pyridine-caffeine interactions are not as strong as caffeine-caffeine interactions, the pyridine-caffeine interactions still significantly disrupted caffeine-caffeine stacking. The alteration of the caffeine-caffeine stacking, occasioned by the presence of pyridine molecules in solution and the consequent formation of heterotactic interactions, leads to the experimentally detected increase in caffeine solubility.

We investigate the effect of several coatings applied in biomedical applications to iron oxide nanoparticles on the size, structure and composition of the particles. The four structural techniques employed - TEM, DLS, VSM, SAXS and EXAFS - show no significant effects of the coatings on the spherical shape of the bare nanoparticles, the average sizes or the local order around the Fe atoms. The NPs coated with hydroxylmethylene bisphosphonate or catechol have a lower proportion of magnetite than the bare and citrated ones, raising the question whether the former are responsible for increasing the valence state of the oxide on the NP surfaces and lowering the overall proportion of magnetite in the particles. VSM measurements show that these two coatings lead to a slightly higher saturation magnetization than the citrate. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazu and Dr. Federica Migliardo. (C) 2016 Elsevier B.V. All rights reserved.

One-dimensional assemblies of magnetic nanoparticles are of great interest from both theoretical and experimental viewpoints. Indeed, new collective physical properties are expected from such organizations, which may lead to innovations especially in the field of life sciences. In this chapter, we first give an overview of the dipolar effects expected to occur in nanoparticle assemblies on the basis of numerical simulation results. Then various assembly strategies are reviewed, as well as some possible resulting applications.

International audience; The drying of complex fluids provides a powerful insight into phenomena that take place on time and length scales not normally accessible. An important feature of complex fluids, colloidal dispersions and polymer solutions is their high sensitivity to weak external actions. Thus, the drying of complex fluids involves a large number of physical and chemical processes. The scope of this review is the capacity to tune such systems to reproduce and explore specific properties in a physics laboratory. A wide variety of systems are presented, ranging from functional coatings, food science, cosmetology, medical diagnostics and forensics to geophysics and art.

We have reanalyzed quasielastic neutron scattering data measured for three prototypical ionic liquids characterized by increasingly longer alkyl chains using two standard models of different complexity. The first one contains only two main components representing a long-range translational diffusion process plus a faster localized-like motion. The second model includes an additional component in order to account for the possibility of having more than one type of localized motion with different characteristic time scales. Our results show the complexity of the relaxation landscape of ionic liquids, indicating that even the more complex model provides only a qualitative average picture of such complex dynamics. The comparison of both models allows to asses also the robustness of the parameters obtained from the fits. Finally the results for the three different ionic liquids are compared in order to determine the effect of the length of the alkyl chain in the translational dynamics of ionic liquids, showing a clear decrease in diffusivity when passing from the ethyl (n=2) to the butyl (n=4) alkyl chain, but a much smaller effect when adding two extra C atoms to the chain.We have reanalyzed quasielastic neutron scattering data measured for three prototypical ionic liquids characterized by increasingly longer alkyl chains using two standard models of different complexity. The first one contains only two main components representing a long-range translational diffusion process plus a faster localized-like motion. The second model includes an additional component in order to account for the possibility of having more than one type of localized motion with different characteristic time scales. Our results show the complexity of the relaxation landscape of ionic liquids, indicating that even the more complex model provides only a qualitative average picture of such complex dynamics. The comparison of both models allows to asses also the robustness of the parameters obtained from the fits. Finally the results for the three different ionic liquids are compared in order to determine the effect of the length of the alkyl chain in the translational dynamics of ionic liquids, showing...

The isothermal dehydration process was investigated by calorimetric experiments on water samples, pointing out a substantial correspondence with gravimetric results, even though the heat flow measurement is characterized by a higher resolution on approaching the end of the evaporation. The role of the geometry of the sample on water evaporation rate is analyzed with reference to two model geometries, resembling the spherical and the planar surface. Specific attention was given to the planar surface for the description of the water evaporation from thin film. The development of a theoretical model, which provides information regarding the water activity, was supported by investigating the effect of the several parameters involved in the isothermal dehydration, such as sample mass and temperature. The data collected revealed some limits in the valuable use of the theoretical model when the experimental conditions are outside the range of quasi-equilibrium thermodynamic condition, e.g., at temperature higher that 50 °C. Attention has also been given to control the initial thermal unbalance in order to improve the measurements.

We present a simple preparation route to obtain a nanoscale metastable hard-magnetic ε-Fe

The influence of water on the relaxation of a prototype ionic liquid (IL) C8mimBF4 is examined in the IL-rich regime combining quasi-elastic neutron scattering (QENS) and molecular dynamics (MD) simulations. The QENS and MD simulations results for relaxation of IL and the equimolar mixture with water probed by the dynamics of the C8mim hydrogen atoms in the time range of 2 ps to 1 ns are in excellent agreement. The QENS data show that translational relaxation increases by a factor of 7 on the addition of water, while rotational relaxation involving multiple processes fitted by a KWW function with low β values is speeded up by a factor of 3 on the time scale of QENS measurements. The MD simulations show that the cation diffusion coefficient, inverse viscosity, and ionic conductivity increase on the addition of water, consistent with the very small change in ionicity. The difficulties in obtaining rotational and translational diffusion coefficients from fits to QENS experiments of pure ILs and IL–water mixt...

It is pointed out that hydrogen/deuterium substitution, frequently used in neutron scattering studies of the structure and dynamics of hydrogenous samples, can have significant effects on structure, phase behavior and protein stability. The effects must be kept in mind in the interpretation of such experiments. In suitable cases, these effects can be mitigated by an appropriate choice of experimental conditions.

The structure of aqueous solutions of methyl β-D-ribofuranoside was investigated by coupling molecular dynamics (MD) simulations and neutron scattering measurements with isotopic substitution. Using a sample of the sugar isotopically-labeled at a single unique position, neutron scattering structure factors and radial distribution functions can be compared with MD simulations constrained to different conformations to determine which conformer best fits the experimental results. Three different simulations were performed with the methyl ether group of the sugar unconstrained and constrained in each of its staggered orientations. The results of the unconstrained simulation showed that the methyl ester group occupied predominantly the 300° position, which is in agreement with the diffraction experimental results. This result suggests that the molecular mechanics force field used in the simulation adequately describes the conformation of the 1-methyl ether group in the methyl β-D-ribofuranoside.

Background This work is focused on mechanisms of uptake in cancer cells of rationally designed, covalently assembled nanoparticles, made of superparamagnetic iron oxide nanoparticles (SPIONs), fluorophores (doxorubicin or Nile Blue), polyethylene glycol (PEG) and folic acid (FA), referred hereinafter as SFP-FA. Methods SFP-FA were characterized by DLS, zetametry and fluorescence spectroscopy. The SFP-FA uptake in cancer cells was monitored using fluorescence-based methods like fluorescence-assisted cell sorting, CLSM with single-photon and two-photon excitation. The SFP-FA endocytosis was also analyzed with electron microscopy approaches: TEM, HAADF-STEM and EELS. Results The SFP-FA have zeta potential below − 6 mW and stable hydrodynamic diameter close to 100 nm in aqueous suspensions of pH range from 5 to 8. They contain ca. 109 PEG-FA, 480 PEG-OCH3 and 22–27 fluorophore molecules per SPION. The fluorophores protected under the PEG shell allows a reliable detection of intracellular NPs. SFP-FA readily enter into all the cancer cell lines studied and accumulate in lysosomes, mostly via clathrin-dependent endocytosis, whatever the FR status on the cells. Conclusions The present study highlights the advantages of rational design of nanosystems as well as the possible involvement of direct molecular interactions of PEG and FA with cellular membranes, not limited to FA-FR recognition, in the mechanisms of their endocytosis. General significance Composition, magnetic and optical properties of the SFP-FA as well their ability to enter cancer cells are promising for their applications in cancer theranosis. Combination of complementary analytical approaches is relevant to understand the nanoparticles behavior in suspension and in contact with cells.

The influence of water on the structure of a prototype ionic liquid (IL) 1-octyl-3-methylimidazolium tetrafluoroborate (C8mimBF4) is examined in the IL-rich regime using high-energy X-ray diffraction (HEXRD) and molecular dynamics (MD) simulations. A many-body polarizable force field APPLE&P was developed for C8mimBF4-water mixture. It predicts structure factors of pure IL and IL-water mixture in excellent agreement with the HEXRD experiments. The MD results provide detailed insights into the structural changes from the partial structure factors, 2-D projections of the simulation box and 3-D distribution functions. Water partitioning with IL and its competition with BF4(-) for complexing the imidazolium rings was examined. The added water molecules occupy a diffuse coordination shell around the imidazolium ring but are not present around the alkyl tail. The strong coordination of the fluorine atoms of the BF4(-) anions to the imidazolium ring is not significantly changed by the addition of water. A complementary packing of water and imidazolium around BF4(-) was found. These results are consistent with the very small differences in the average structure between the pure IL and the mixture.

Molecular dynamics simulations were carried out on several systems of caffeine interacting with simple sugars. These included a single caffeine molecule in a 3 molal solution of α-D-glucopyranose, at a caffeine concentration of 0.083 molal; a single caffeine in a 3 molal solution of β-D-glucopyranose, and a single caffeine molecule in a 1.08 molal solution of sucrose (table sugar). Parallel Nuclear Magnetic Resonance titration experiments were carried out on the same solutions under similar conditions. Consistent with previous thermodynamic experiments, the sugars were found to have an affinity for the caffeine molecules in both the simulations and experiments, and that the binding in these complexes occurs by face-to-face stacking of the hydrophobic triad of protons of the pyranose rings against the caffeine face, rather than by hydrogen bonding. For the disaccharide, the binding occurs via stacking of the glucose ring against the caffeine, with a lesser affinity for the fructose observed. These findings are consistent with the association being driven by hydrophobic hydration, and are similar to the previously observed binding of glucose rings to various other planar molecules, including indole, serotonin, and phenol.

In this work, the new refined mineral platelets-like morphology of simonkolleite based particles described by Shemetzer et al. (1985) were synthesized in zinc nitrate aqueous solution by a moderate solution process. The morphological and structural properties of the platelets-like Zn 5 (OH) 8 Cl 2 ·H 2 O were characterized by scanning electron microscope energy dispersed X-ray spectroscopy, transmission electron microscope, powder X-ray diffraction and selected area electron diffraction as well as attenuated total reflection infrared spectroscopy. The morphology as well as the size in both basal and transversal directions of the simonkolleite Zn 5 (OH) 8 Cl 2 ·H 2 O nano/micro crystals was found to be significantly depending on the specific concentration of 0.1 M of Zn 2+ /Cl − ions in the precursor solution. The simonkolleite Zn 5 (OH) 8 Cl 2 ·H 2 O nano-platelets revealed a significant and singular H 2 gas sensing characteristics. The operating temperature was found to play a key role on the sensing properties of simonkolleite. The effect of temperature on the simonkolleite sample as a hydrogen gas sensor was studied by recording the change in resistivity of the film in presence of the test gas. The results on the sensitivity and response time as per comparison to earlier reported ZnO based sensors are indicated and discussed.

International audience; We report the efficient one-step synthesis and detailed physicochemical evaluation of novel biocompatible nanosystems useful for cancer therapeutics and diagnostics (theranostics). These systems are the superparamagnetic iron oxide nanoparticles (SPIONs) carrying the anticancer drug doxorubicin and coated with the covalently bonded biocompatible polymer poly(ethylene glycol) (PEG), native and modified with the biological cancer targeting ligand folic acid (PEG-FA). These multifunctional nanoparticles (SPION-DOX-PEG-FA) are designed to rationally combine multilevel mechanisms of cancer cell targeting (magnetic and biological), bimodal cancer cell imaging (by means of MRI and fluorescence), and bimodal cancer treatment (by targeted drug delivery and by hyperthermia effect). Nevertheless, for these concepts to work together, the choice of ingredients and particle structure are critically important. Therefore, in the present work, a detailed physicochemical characterization of the organic coating of the hybrid nanoparticles is performed by several surface-specific instrumental methods, including surface-enhanced Raman scattering (SERS) spectroscopy, X-ray photoelectron spectrometry (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). We demonstrate that the anticancer drug doxorubicin is attached to the iron oxide surface and buried under the polymer layers, while folic acid is located on the extreme surface of the organic coating. Interestingly, the moderate presence of folic acid on the particle surface does not increase the particle surface potential, while it is sufficient to increase the particle uptake by MCF-7 cancer cells. All of these original results contribute to the better understanding of the structure–activity relationship for hybrid biocompatible nanosystems and are encouraging for the applications in cancer theranostics.

Extended planar hydrophobic surfaces, such as are found in the side chains of the amino acids histidine, phenylalanine, tyrosine, and tryptophan, exhibit an affinity for the weakly hydrated faces of glucopyranose. In addition, molecular species such as these, including indole, caffeine, and imidazole, exhibit a weak tendency to pair together by hydrophobic stacking in aqueous solution. These interactions can be partially understood in terms of recent models for the hydration of extended hydrophobic faces and should provide insight into the architecture of sugar-binding sites in proteins.

Molecular dynamics simulations were carried out on a system of eight independent caffeine molecules in a periodic box of water at 300 K, representing a solution near the solubility limit for caffeine at room temperature, using a newly-developed CHARMM-type force field for caffeine in water. Simulations were also conducted for single caffeine molecules in water using two different water models (TIP3P and TIP4P). Water was found to structure in a complex fashion around the planar caffeine molecules, which was not sensitive to the water model used. As expected, extensive aggregation of the caffeine molecules was observed, with the molecules stacking their flat faces against one another like coins, with their methylene groups staggered to avoid steric clashes. A dynamic equilibrum was observed between large n-mers, including stacks with all eight solute molecules, and smaller clusters, with the calculated osmotic coefficient being in acceptable agreement with the experimental value. The insensitivity of the results to water model and the congruence with experimental thermodynamic data suggest that the observed stacking interactions are a realistic representation of the actual association mechanism in aqueous caffeine solutions.

International audience; Molecular dynamics simulations have been conducted of the helical polypeptide melittin, in concentrated aqueous solutions of the alpha and beta anomers of D‐glucopyranose. Glucose is an osmolyte, and it is expected to be preferentially excluded from the surfaces of proteins. This was indeed found to be the case in the simulations. The results indicate that the observed exclusion may have a contribution from an under‐representation of hydrogen bonding interactions between glucose groups and exposed side chains, compared to water. However, glucose was found to bind quite specifically to melittin by stacking its hydrophobic face, consisting of aliphatic protons, against the flat hydrophobic face of the indole group of the tryptophan‐19 side chain. Although the binding site for this interaction is localized, the binding is weak for both anomers, with a binding free energy estimated as only ∼0.5 kcal/mol (i.e. near kBT). The face of the sugar stacked against the Trp indole ring is different for the two anomers of glucose, due to the disruption of the H1‐H3‐H5 hydrophobic triad of the beta anomer by the axial C1 hydroxyl group in the alpha anomer. The measurable affinity of the sugar for the Trp side chain is consistent with the very frequent occurrence of this group in the binding sites of proteins that complex with sugars.

International audience; We report electron magnetic resonance (EMR) and magnetooptical studies of borate glasses of molar composition 22.5K2O-22.5Al2O3-55B2O3 co-doped with low concentrations of Fe2O3 and MnO. In as-prepared samples the paramagnetic ions, as a rule, are in diluted state. However, in the case where the ratio of the iron and manganese oxides in the charge is 3/2, magnetic nanoparticles with characteristics close to those of manganese ferrite are formed already at the first stage of the glass preparation, as evidenced by both magnetic circular dichroism (MCD) and EMR. After thermal treatment all glasses show characteristic MCD and EMR spectra, attesting to the presence of magnetic nanoparticles, predominantly including iron ions. Preliminary EXAFS measurements at the FeK-absorption edge show an emergence of nanoparticles with a structure close to MnFe2O4 after annealing the glasses at 560 1C. By computer simulating the EMR spectra at variable temperatures, a superparamagnetic nature of relatively broad size and shape distribution with the average diameter of ca. 3-4 nm. The characteristic temperature-dependent shift of the apparent resonance field is explained by a strong temperature dependence of the magnetic anisotropy in the nanoparticles. The formation of magnetic nanoparticles confers to the potassium-alumina-borate glassesmagnetic and magneto-optical properties typical of magnetically ordered substances. At the same time, they remain transparent in a part of the visible and near infrared spectral range and display a high Faraday rotation value.

We present results of parallel quasielastic neutron scattering (QENS) experiments and molecular dynamics numerical simulations for the dynamics of a prototype ionic liquid, 1-ethyl-3-methyl-imidazolium bromide. Differences and similarities with those from the crystal phase are also discussed. Both experiment and simulation demonstrate that, in the length and time scales being probed here (fractions of a nm and a few ps), the dynamics are dominated by activated translational diffusion in the liquid phase and reorientations of the ethyl groups in both solid and liquid.

Neutron diffraction with isotopic substitution (NDIS) experiments have been used to examine the structuring of aqueous solutions of pyridine. A new method is described for extracting the structure factors relating to intermolecular correlations from neutron scattering experiments on liquid solutions of complex molecular species. This approach performs experiments at different concentrations and exploits the intramolecular coordination number concentration invariance (ICNCI) to separate the internal and intermolecular contributions to the total intensities. The ability of this method to deconvolute molecular and intermolecular correlations is tested and demonstrated using simulated neutron scattering results predicted from molecular dynamics simulations of aqueous solutions of the polyatomic solute pyridine in which the inter- and intramolecular terms are known. The method is then implemented using neutron scattering measurements on solutions of pyridine. The results confirm that pyridine shows a significant propensity to aggregate in solution and demonstrate the prospects for the future application of the ICNCI approach to the study of large polyatomic solutes using next-generation neutron sources and detectors.

We tried to produce polystyrene (PS) nanoparticles with a controlled mesoporosity by a new route of synthesis. Starting from internally self-organized emulsions containing a hexagonal or a micellar phase, we then polymerized the internal phase of the droplets containing styrene by UV. We managed to produce one type of polystyrene nanoparticles, from the partial polymerization of the micellar phase, down to a diameter of 60 nm. The final size of the solid nanoparticles is controlled by the size of the emulsion prior to polymerization and depends on the stabilizer content. Contrary to the preparation of microporous or mesoporous silicates, our procedure does not need further purification, removal of solvent or high temperature oxidation. We also present the reasons why we could not polymerize the hexagonal phase droplets at the moment.

Using a simple route for preparing uniform spherical mesoporous MCM-41 materials based on a one-step synthesis in an all-water medium, we have investigated the effects of changes of the surfactant composition. The morphology, texture and structure of five samples with different compositions reveal that both, the external organization and internal pore structure, are governed by the silicate:surfactant ratio. The intake of fluids into the pores—an important issue for the use of this material in biotechnology such as localized drug delivery, vectorization of drugs, biosensing applications, and biochemical separations—was checked and confirmed.

Reinforcement of natural rubber was achieved using carboxylated multiwalled carbon nanotubes (c-MWCNT) dispersed with sodium dodecyl sulfate. The structure of the reinforced latex films was investigated by TEM and AFM. The tensile and dynamic-mechanical tests demonstrated a strong enhancement in the Young’s modulus (∼10-fold), tensile strength (∼2-fold) and storage modulus (∼60-fold) at low-strain in the rubbery state with up to 8.3 wt% of MWCNTs, with a small reduction in elongation at break. Dielectric measurement at room temperature revealed a low percolation threshold (

The atomic structures of liquid Si metal and SiGe alloy in the normal and supercooled liquid states have been measured by X-ray diffraction from aerodynamically levitated and laser heated liquid droplets. The measurements covered a wide range of scattering vector Q (0.8–20 A −1 ) and a wide temperature range that extended into the supercooled region. The present results on liquid Si confirm earlier measurements that showed a decrease in first-shell coordination with increased supercooling. For liquid SiGe, the shoulder on the high- Q side of the first peak in the structure factor S ( Q ) sharpens with increased supercooling, suggesting an increase in covalent bonding and development of chemical short-range order.

Disorder among surface spins is a dominant factor in the magnetic response of magnetic nanoparticle systems. In this work, we examine time-dependent magnetization in high-quality, monodisperse hollow maghemite nanoparticles (NPs) with a 14.8 ± 0.5 nm outer diameter and enhanced surface-to-volume ratio. The nanoparticle ensemble exhibits spin-glass-like signatures in dc magnetic aging and memory protocols and ac magnetic susceptibility. The dynamics of the system slow near 50 K and become frozen on experimental time scales below 20 K. Remanence curves indicate the development of magnetic irreversibility concurrent with the freezing of the spin dynamics. A strong exchange-bias effect and its training behavior point to highly frustrated surface spins that rearrange much more slowly than interior spins. Monte Carlo simulations of a hollow particle corroborate strongly disordered surface layers with complex energy landscapes that underlie both glass-like dynamics and magnetic irreversibility. Calculated hysteresis loops reveal that magnetic behavior is not identical at the inner and outer surfaces, with spins at the outer surface layer of the 15 nm hollow particles exhibiting a higher degree of frustration. Our combined experimental and simulated results shed light on the origin of spin-glass-like phenomena and the important role played by the surface spins in magnetic hollow nanostructures.

International audience; The solvation of caffeine in water is examinedwith neutron diffraction experiments at 353 K. Theexperimental data, obtained by taking advantage of isotopicH/D substitution in water, were analyzed by empiricalpotential structure refinement (EPSR) in order to extractpartial structure factors and site−site radial distributionfunctions. In parallel, molecular dynamics (MD) simulationswere carried out to interpret the data and gain insight into the intermolecular interactions in the solutions and the solvationprocess. The results obtained with the two approaches evidence differences in the individual radial distribution functions,although both confirm the presence of caffeine stacks at this temperature. The two approaches point to different accessibility ofwater to the caffeine sites due to different stacking configurations.

Recent progress in the synthesis and applications of MCM-41 based mesoporous materials is reviewed. Since the independent discovery in the early 1990s by groups in the Japan and USA of the formation of mesostructured silica using surfactants as structure directing agents, a variety of alternative synthesis routes have been proposed. These include the use of ionic (both cationic and anionic) surfactants, neutral surfactants based on block and star diblock copolymers, non-surfactant organic compounds and the Stober process for synthesizing silica spheres. The unique properties of MCM-41 based silica materials make them attractive candidates for applications in catalysis, production of novel materials by encapsulating metals, semiconductors and biofluids. Particular attention is given to the use of these composites in biotechnology including biosensors, biocatalysis and drug delivery.

Stretched exponentials are often used to describe quasi-elastic neutron scattering (QENS) and nuclear magnetic resonance (NMR) relaxation data from polymer melts. In this paper, we attempt to derive a more physically meaningful model of the local (∼0.1 nm), short-time (∼10 ps) dynamics of linear polymers that takes into account (i) orientational diffusion along the polymer chain, (ii) local conformational transitions, and (iii) long-time, large-scale motions. The model takes into account the spatial component of the local dynamics, described in terms of the scattering vector Q. The model is applied to QENS results on highly entangled polyethylene oxide (PEO) melt at 373 K. We find the Q dependences of the three correlation times of the model to be consistent with Q°, Q -2 and Q -4 power laws, respectively. The high-Q limit of the model closely resembles the NMR-based DLM model (Dejean de la Batie et al 1988 Macromolecules 21 2045) but the physical interpretation is different. At 373 K, the polymer dynamics is described in terms of transverse motions of the chain segments over a distance of a few nm, with a local monomeric diffusion coefficient of 1.78 x 10 -9 m 2 s -1 . From this value, we derive a monomeric friction coefficient ξ 0 = 2.89 x 10 -12 N s m -1 that, used as numerical input to the Doi-Edwards theory, leads to a chain centre-of-mass diffusion coefficient D cm = 9.4 x 10 -15 m 2 s -1 . This value is in good agreement with pulsed field gradient NMR data (Appel and Fleischer 1993 Macromolecules 26 5520) and validates the proposed model.

The dynamical structure factors of supercooled-liquid and hot-solid silicon are measured by inelastic X-ray scattering at the same temperature, 1620 K. Two significant changes in the averaged longitudinal sound velocities and in the longitudinal modulus are observed. First, we observe a different longitudinal modulus in the polycrystalline hot-solid silicon compared to the extrapolated value obtained from the single-crystal measurement. This reduction of the modulus may be a precursor of the semiconductor-to-metal transition. Second, the increase in the longitudinal modulus in the liquid upon supercooling is consistent with an increase in the degree of the directional bonding.

Neutron diffraction with isotopic substitution (NDIS) experiments and molecular dynamics (MD) simulations have been used to examine the pentose D-xylose in aqueous solution. By specifically labeling D-xylose molecules with a deuterium atom at the nonexchangeable hydrogen position on C4, it was possible to extract information about the atomic structuring around just that specific position. The MD simulations were found to give satisfactory agreement with the experimental NDIS results and could be used to help interpret the scattering data in terms of the solvent structuring as well as the intramolecular hydroxyl conformations. Although the experiment is challenging and on the limit of modern instrumentation, it is possible by careful analysis, in conjunction with MD studies, to show that the conformation trans to H4 at 180 degrees is strongly disfavored, in excellent agreement with the MD results. This is the first attempt to use NDIS experiments to determine the rotameric conformation of a hydroxyl group.

The use of containerless techniques enables studies of materials above the melting point and in the supercooled state with a high degree of control. In particular, the atomic structure of liquid materials can be determined by measurements of the X-ray structure factor S(Q) and calculation of the corresponding pair correlation function g(r). At high temperature, it is useful to reduce the acquisition times in order to avoid sample deterioration or instabilities. To do that, different solutions can be used: use of a conventional detector at a third generation source, which provides intense X-ray beams leading to reduced acquisition times, use of image-plate scanners which enable short counting times with good statistics, and use of a wide-angle position-sensitive detector which is better for time-resolved studies. We show that these three approaches are complementary for studies at high temperatures.

We compare the departure from gaussian (harmonic) behavior of the dynamic structure factors of a sample showing two glassy phases one of those being an orientationally-disordered crystal. The deviations from harmonic behavior of the amorphous phase and disordered crystal are found to be remarkably close. Such proximity enables us to take advantage of the crystal symmetry to relate specific details of the inter-particle potential to the non-gaussian effects characteristic of glassy matter.

We introduce novel materials consisting of hydrated titanium oxide nanotubes filled with poly(ethylene oxide) (PEO) via a simple synthesis route. MAS NMR, TEM, TGA, PAS-FTIR, and ATR-FTIR measurements provide clear evidence of polymer inclusion in these nanotubes. PEO has been widely studied in the field of solid-state electrolytes, and its behavior in this confined environment shows unusual properties: faster relaxation times (as seen by PFGSE-NMR) and absence of transitions in DSC data, two criteria that hint of a potential enhancement of segmental mobility controlling ion diffusion. Conversely, the polymer serves as an efficient template when the inclusion compound is pyrolyzed to yield well-defined TiO2 nanorods.

The effects of the solution of glucose molecules on the dynamics of solvent water have been studied by quasielastic neutron scattering (QENS) measurements on solutions of selectively deuterated glucose in natural water. The data are fitted to two Lorentzians ascribed to pure translational and mixed translational and rotational character, respectively. The addition of the glucose to the water causes a substantial slowing down, by a factor 10 for the translational diffusion and 3−4 for the rotational motion at the highest concentration studied, 1:11 C6H12O6:H2O. The values obtained for water diffusion constants are consistent with previous QENS and NMR experiments on monosaccharide solutions but an order of magnitude higher than those derived from a recent molecular dynamics simulation.

Silver iodide nanoparticles were prepared by mixing two microemulsions containing the precursor salts, silver nitrate and potassium iodide. Five values of w=[water]/[surfactant] were used, namely 2, 4, 8, 16, and 32. Transmission electron microscopy (TEM) showed that the nanoparticle diameters were 4–240 nm and increased proportionally with w. The nanoparticles prepared from a microemulsion of w=2 and 8 showed brown and ocherous colors respectively, while bulk silver iodide powder is pale yellow. The crystal structure was determined by neutron powder diffraction. The composition was estimated to be 25% β-AgI and 75% γ-AgI. The super-ionic conductor phase could not be detected at room temperature. The w=8 microemulsion was examined with small-angle neutron scattering (SANS) in order to study the core-shell structure of the reverse micelles at various temperatures. Measurements were carried out at 20 and 9 °C and then at 70 °C and finally at 28 °C, in order to investigate whether the structural changes were reversible with temperature. The total radius of the micelles, surfactant shell thickness and water core radius decreased with increasing temperature and the changes were reversible with temperature. The particle diameters derived by TEM were generally larger than those estimated from the SANS measurements. This suggested that the silver iodide nuclei formed initially grew to reach a certain size, corresponding to the most thermodynamically stable species in the microemulsion, because of the fast exchange between the water cores.

Neutron diffraction experiments were carried out at ambient temperature on aqueous solutions of glucose at concentrations of 1, 3, and 5 molal. The difference methods of neutron diffraction and isotopic substitution were used to determine various structure factors associated with all the exchangeable hydrogen atoms of the solutions. The results imply that the hydration of the glucose molecule is not concentration sensitive. It is also found that the average water structure itself is relatively unperturbed by the presence of glucose.

Small-angle and quasielastic neutron scattering measurements have been carried out on mixtures of 3-methylpyridine/heavy water (3MP/HW). Depending upon the relative concentration these mixtures are fully miscible or show a closed-loop phase diagram. Two mixtures corresponding to the fully miscible composition as well as a phase-separating sample are studied together with neat 3MP liquid. The SANS results show relatively large coherence lengths even for the miscible binary liquid. Quasielastic neutron scattering reveals a significant slowing down of the 3MP dynamics within the mixture as compared to that of pure 3MP. As the phase-separation line is approached from below the translational diffusion coefficients show a clear signature of critical slowing down that mimics the behavior of the shear viscosity.

In a single diffraction measurement, on a multi-component high-temperature liquid, the measured S(Q) and G(r) are weighted averages of the partial functions for the different atom pairs, and different structural models can be consistent with the experimental data. In order to obtain more specific structural information, we have combined aerodynamic levitation and laser heating with the anomalous x-ray scattering technique to study the structure of liquid yttrium oxide at high temperature. The results are in good agreement with the previous experiments and computer simulations. This combination represents a powerful technique for obtaining reliable partial structure information in complex high-temperature liquid materials.

This work reviews progress in the field of the dynamics of disordered condensed matter, encompassing materials where at least one component lacks either rotational or translational long-range order. Systems in thermodynamic equilibrium as well as those where some aspect of the disorder is frozen into a glassy state are discussed. The most relevant experimental methods are reviewed, as well as recent advances in computer simulation, which is becoming increasingly important in this field. Examples of recent applications of these techniques to study the various aspects of dynamical disorder are then provided. The final section highlights common features of the dynamics exhibited by different systems, and discusses prospects for the future development of the field.

The principles for simultaneous measurements of the electrical conductivity and the permeability of materials ranging from ionic to semiconductors to insulators, using a non-invasive, electrodeless method, are presented succinctly. Recent results obtained for a variety of materials at room temperature and at the melting point illustrate the validity of the method. Special emphasis will be given to the fact that transport properties are now accessible over a regime of temperature never achieved before. Of particular interest is the fact it is now possible to monitor the inductance as a function of cooling, allowing a determination of changes accompanying the electrical properties and the magnetisation in the liquid and supercooled states.

To explore quantum effects on the structure of liquid water, we have carried out high-energy x-ray diffraction measurements of quantum differences both under isothermal conditions at 24.5 °C and under isochoral conditions at 0.0997 atom/A3. The measured isothermal difference correlation function is approximately equivalent to an isochoric temperature differential (ITD) of 5.5 °C, reflecting the tendency of quantum effects to introduce more disorder into the liquid. The measured isochoral correlation function is about three times higher in amplitude and is approximately equivalent to an ITD of 19 °C. Since the isochoral measurements for H2O and D2O were made at temperatures 13.5 °C apart, the isothermal and isochoral functions are roughly consistent. The discrepancies are discussed with reference to data on the pressure dependence in the literature. They are comparable with differences in results obtained with different potential functions in path-integral molecular dynamics simulations. The present result...